Superheterodyne Shortwave Receiver

This will be a very short post showcasing a Telecommunications project that I completed for school. I'm reluctant to share any of the specs, as the circuit board and specifications were developed by one of the faculty at the school, and I don't really feel that they are mine to share. BUT, feel free to take a look at it!

This entire project is based around the TDA1572 IC, which is an older chip designed for AM radio receivers. In this project, the radio is tuned to function between ~ 9-12MHz. It does work well, and late at night I can listen to international transmissions! I'm listening to China Radio International while writing this! It also feature an MPF102 JFET and an LM386 OPAMP for the amplification of the signal. It also has 3 hand wound toroids.

The electronics are housed in this cigar box, which at one point contained 25 Luis Martinez Ashcroft Corona cigars (A year in the humidor and they really have a nice medium taste, I like them with a drink of wine or Scotch at night). This was the perfect size for this radio project. Buy your box here!

This view is to show off the speaker. It's a clear plastic waterproof speaker I picked up at the surplus store, I may replace it later, but it works fine. On the bottom left you can see a banana terminal, which I'm using to insert the antenna. Currently I'm using a length of scrap clothes line which works very well. I clip the antenna to my clothes line and reel it out, which works great for a temporary whip antenna, it's about 35'. A longer antenna would be better for this radio, but it works quite well!

While I was making my youtube video, my cat decided to come help.

  

Here is a picture of the guts. The board was created for a class to use, which included instructions. The TDA1572 was an SMD chip chip soldered on its own board, then that board was soldered using headers to the main board.
A lot of the schematic can be found on the data sheets provided by the futurlec website, the data sheet is very detailed, and has lots of room for deciding how you want to build your radio!
You can can also see the potentiometers I hot glued in (the box was too thick to set the nut). The potentiometers are for volume, fine tune, coarse tune. You can also see a few marrettes, which are used to connect the wallwart to the board. The board has a 7805 regulator.

For a handmade project, I think it looks pretty slick!

Okay, so what's this superheterodyne talk about? The TDA1572 IC allows for a lot of the work to be integrated into one chip. In most hobby radios, or super old radios, a system called RTF (Radio Tuned Frequency) is used, which usually uses a ferrite road wound with a given number of turns of magnet wire, and a costly variable capacitor, which then resonates with the desired frequency, and that signal is amplified. The superheterodyne takes a signal and brings it down to the IF (intermediate frequency) or "working frequency" and then does its work. This chip requires relatively few components for what it is doing!

If you are interested in the work being done on the signal in a superheterodyne receiver, check out the wikipedia page, it is very descriptive and well written.
I am very impressed with how radio has progressed. I intend to build an FM receiver into my next project, and the number of external components is almost none! That project will just drop the FM IC onto an I2C bus, and away it goes. I do think in the future I will pick up a vintage radio and claim the parts to build an RTF style receiver that goes even lower down so I can explore some of the transmissions happening further down, but that might be a while before that happens...

Anyway, for anyone who is interested, I'm still working on my IV-9 clock, and very recently I made the small step of getting my two tube counter to work on a PIC18F44K22! Which I plan on the final clock radio to run entirely on one PIC18F45K22 microcontroller. I'm still toying with it, hopefully I'll have a 6 tube board going soon.

 Here are the two tubes displaying 27, while you can see it toggling between the two tubes on the scope. I had a few issues with the software going from Arduino to Microchip, but yeah, works fine.


Anyway, cheers, have a good one!